1. Field of the Invention
Embodiments of the invention generally relate to an apparatus and method of use in an internal combustion engine. More particularly, embodiments of the invention relate to a combustion chamber design that physically segregates the chamber into multiple smaller chambers during combustion in a combustion engine.
2. Description of the Related Art
Conventional combustion, reciprocating engines are widely used as automotive engines. These engines are designed to work on a predetermined mixture of air and fuel, which is ignited by an ignition plug, such as a spark plug or a glow plug, in a combustion chamber.
FIG. 1 is a cross-sectional view of a conventional power cylinder assembly 50. The power cylinder assembly 50 includes a cylinder 110, a piston 100, a cylinder head 117, valves 140 and 150, an ignition plug 160, and manifolds 145 and 155. A combustion chamber 115 is defined by an inner wall 111 of the cylinder 110, the crown or top surface 107 of the piston 100, along with the cylinder head 117. The piston 100, which is slideably disposed in the cylinder 110, and the inner wall 111 of the cylinder 110 are generally cylindrical in shape. The piston 100 includes several compression seals 120 (commonly referred to as piston rings) disposed within annular grooves 122 on an outer surface 124 of the piston 100 to keep the fuel/air mixture (hereinafter xe2x80x9cmixturexe2x80x9d) within combustion chamber 115. Additionally, the piston 100 includes an aperture 105 for connecting the piston to a connecting rod (not shown), whereby the piston may be moved in a reciprocating fashion (e.g., axially within the cylinder 110). The movement of the piston 100 is translated to the rod, which provides power to an engine crank shaft (not shown). The intake manifold 145 delivers the mixture to the combustion chamber 115 and the intake valve 140 regulates the amount of mixture that enters the chamber. The ignition plug 160 ignites the mixture in the combustion chamber 115 and produces a combustion flame. The exhaust valve 150 and the exhaust manifold 155 exhaust the burned mixture and any remaining mixture from the chamber 115.
Typically, an engine cycle starts with an intake stroke, wherein the mixture is delivered into the combustion chamber 115. During the intake stroke, the piston 100 descends to bottom dead center or the lowest point that the piston may travel in the cylinder 110. At this point, the intake valve 140 opens and supplies the combustion chamber 115 with the appropriate amount of mixture through the intake manifold 145. During the intake stroke, the exhaust valve 150 remains closed. As the mixture enters the combustion chamber 115, a swirl, which mixes the air and fuel, is created by the positioning of the intake valve 140 at a certain angle in the cylinder head 117. Further, the swirl may be utilized to create turbulence for combustion enhancement. After the piston 100 reaches bottom dead center, the intake valve 140 is closed and ends the intake stroke. The compression stroke begins when the piston 100 ascends in the cylinder 110. The compression stroke compresses the mixture for better combustion. In the compression stroke, the piston 100 ascends in the cylinder 110 and causes the mixture to squish or move radially inward, causing a squish flow. The squish flow helps to promote faster combustion by enhancing flame propagation. Before the piston 100 reaches top dead center, or the highest point that the piston can travel in the cylinder, an ignition plug 160 is fired to ignite the mixture. In diesel engines, no ignition plug is present, but instead, ignition can occur when the compression pressure and temperature in the chamber is sufficient to support ignition. The pressure and temperature in the combustion chamber 115 are increased by the burning mixture and the pressure forces the piston 100 to descend during the expansion stroke, which moves the connecting rod to power the engine. The expansion stroke provides power to the engine. The piston 100 reaches bottom dead center and ends the expansion stroke. The exhaust stroke, which removes the combusted mixture from the chamber 115, begins when the piston 100 ascends in the cylinder 110. As the piston 100 ascends, the exhaust valve 150 opens to remove the combustion by-products and any remaining mixture through the exhaust manifold 155. The cycle is then repeated.
The efficiency of the combustion chamber to combust the mixture determines the amount of pollutants such as oxides of nitrogen or NOx that are released into the atmosphere. To achieve higher efficiency using hydrocarbon fuels, leaner fuel to air ratios have been utilized. For equivalent power output, a leaner fuel to air ratio must be accompanied by a higher over-all airflow to the engine. The leaner fuel to air ratio leads to high thermal efficiencies, when the airflow has been compensated, and to higher peak temperatures. At higher peak temperatures, combustion efficiency improves at the expense of increased production of NOx. It is known that above 1300-1500xc2x0 K. (Kelvin), NOx production increases greatly; hence it is desirable to control the peak temperature below this range. Additionally, faster flame propagation speed increases engine thermal efficiency, but can cause knock (commonly referred to as auto ignition). Knock occurs when the chemical kinetic reactions within the unburned mixture spontaneously ignite during the engine cycle. Typically, knock is initiated by compression of the unburned mixture during the combustion portion of the engine cycle. After the spark ignition process, the unburned mixture is subjected to compression by the combined effects of piston""s motion and flame propagation. If the flame produced by the ignition plug fails to consume the entire unburned mixture before compression-induced chemical reactions cause spontaneous ignition within the unburned mixture, knock will occur. Hence, control of the propagation of the flame has a direct impact on the propensity for a given engine to knock. Knock decreases combustion efficiency because the energy created during auto ignition is uncontrolled and can lead to catastrophic engine failure.
In a conventional combustion chamber, the squish region, where squish flow is created, may be up to 70% of the crown""s surface and is a continuous region. Because the squish region is one, large continuous area, there is more area for a flame to lose energy into the piston and quench due to wall heat transfer losses. Additionally, the flame tends to extinguish by the time it reaches the outer portion of the squish region, thereby leaving some mixture unburned leading to combustion inefficiency.
In engines, a brake mean effective pressure (BMEP) is generated within the combustion chamber as a resultant pressure force produced from the controlled burning of the mixture. High BMEP is associated with high power output and high engine efficiency. In conventional high BMEP applications, the ignition plug is fired at a relatively high pressure and temperature. However, firing at higher pressure decreases the life of the ignition plug. In order for the ignition plug to last longer, it should be fired at a lower pressure than the pressure required in conventional engine designs used in high BMEP applications. However, if the ignition plug is fired at a lower pressure or earlier ignition timing (advanced ignition timing), the productions of knock and NOx emissions increase.
Various attempts have been made to improve combustion chambers for use with lean mixtures to reduce concentrations of NOx and knock. U.S. Pat. No. 5,224,449 discloses using a toroidal chamber on the crown of the piston, whereby a mixture is ignited in the main chamber then reaches the toroidal chamber and ignites the fuel in the toroidal chamber. The pressure in the toroidal chamber increases, whereby a combustion jet gas is shot into the main chamber causing a turbulence that mixes and combusts the mixture. However, the temperatures and pressures produced in the toroidal chamber are so great, that damage to the toroidal chamber of the piston, may occur, leading to catastrophic engine failure. Additionally, the high flame temperature can""t be controlled leading to increased NOx production. U.S. Pat. No. 4,920,937 includes a combustion chamber having a squish region for generating a squish flow. The squish flow helps to propagate flame speed from the spark plug to the main chamber for better combustion efficiency. However, the increased flame speed can increase undesired knock and decrease engine efficiency. Additionally, because the squish area of the squish region is relatively large, the flame can extinguish before reaching the mixture remaining in the squish region, leading to increased uncombusted or unburned hydrocarbons.
Therefore, there is a need for a combustion chamber that can efficiently combust a fuel/air mixture, while reducing the production of air pollutants.
Embodiments of the present invention generally provide for an improved method and combustion chamber for use in a combustion engine that is segregated into multiple chambers to control peak pressure and temperature and to control flame propagation speed to reduce knock.
In one embodiment, a combustion apparatus having a combustion chamber is provided. The combustion chamber preferably includes a cylinder having an inner wall and a cylinder head, and a piston disposed in the cylinder. The piston preferably has a top surface having at least a first and a second chamber being concentric about a central axis of the piston. The first and second chambers can be annular recessed grooves, circular recesses or a combination thereof. An inner annular portion is formed between the at least first and the at least second chambers. Additionally, an outer raised portion is formed between the at least second chamber and a perimeter of the piston. The combustion apparatus further includes an intake valve and an intake manifold disposed in the cylinder head and in communication with the combustion chamber. Further, an exhaust valve and exhaust manifold are disposed in the cylinder head and in communication with the combustion chamber. Additionally, an ignition device is disposed in the cylinder head and extends into the combustion chamber.
In another embodiment, a piston for an internal combustion engine is provided and preferably includes a cylindrical body that has a surface that defines a region of a combustion chamber, wherein the surface includes at least one circular recessed portion and at least one annular recessed groove being concentric about a central axis of the cylindrical body. The at least one circular recessed portion may be separated from the at least one annular recessed groove by an inner annular raised portion. Additionally, the at least one annular recessed groove is separated from a perimeter of the surface by an outer annular raised portion.
In still another embodiment, the piston includes a surface that defines a portion of the combustion chamber. The surface includes a chamber that has a partition dividing the chamber into approximately equal sized first and second chambers. The partition can act as flame control portion that directs the flame from one chamber into another and controls the flame propagation speed.
In a further embodiment, a combustion apparatus is provided having a cylinder head that includes a surface that defines a combustion chamber. The surface can include at least one circular recess and at least one annular recessed groove being concentric about the central axis of the cylinder head. The at least one circular recess may be separated from the at least one annular recessed groove by an inner annular raised portion. Additionally, the at least one annular recessed groove is separated from a perimeter of the surface by an outer annular raised portion.
In still a further embodiment, an apparatus for use in a combustion engine is provided that includes a cylinder head having a surface defining a portion of a combustion chamber, the surface having a chamber formed therein. A partition divides the chamber into approximately equal sized first and second chambers. The partition can act as a flame control portion that directs the flame from one chamber into another and controls the flame propagation speed.
A method for efficiently combusting a mixture of fuel and air in a combustion chamber is also provided and can include the steps of admitting a mixture of fuel and air into the combustion chamber having a surface that includes at least a first chamber concentric with a central axis of the surface and at least a second chamber concentric with the central axis; and controlling a peak temperature and pressure of the combustion chamber by first igniting the mixture in the at least first chamber and producing a combustion flame, then igniting the mixture in the at least second chamber by the combustion flame thereby, producing the peak temperature and pressure in the combustion chamber. The method can also include controlling the flame propagation speed to reduce knocks and pollutants, with the inner and outer annular raised portions and their walls, and can further include controlling turbulence within the combustion chamber by providing separate squish portions designed to optimize turbulence in each of the separate combustion chambers. The method can also include controlling the peak temperature and pressure to decrease the production of pollutants by maintaining the temperature less than about 1,300xc2x0 K. to 1,500xc2x0 K. and/or by establishing a size and shape of the at least first and second chambers. By controlling the peak temperature and pressure, the life the ignition plug can increase by firing it at lower peak pressure.